Conventionally postal franking machines have included a printing cylinder which bears the semi-permanent information to be applied by overprinting to an envelope together with a plurality of selectable printing devices for printing variable insertions into the permanent information such as the date and the amount of the prepaid postage applicable. A relatively complex mechanism has consequently been needed to effect variation of the selectable printing devices which have had to be located within the cylinder.
Furthermore, any change in the semi-permanent information (for example to introduce current advertising material into the data to be printed on the envelope) has often necessitated major changes to the cylinder and the replacement of at least part of the latter with fresh sectors containing the new typeface.
It is an object of the present invention to provide an improved postal franking machine in which changes in the content of the printed material can be made more easily than hitherto.
A further difficulty associated with the franking of envelopes concerns the frequently very uneven thickness of the latter across the width of the region to which the printed matter is to be applied.
Accordingly it is a subsidiary feature of the invention to provide an improvement in the design of postal franking machines which will allow for such uneveness in envelopes to be printed.